1. Field of the Invention
The present invention relates to a surface-protecting film to be permanently or semipermanently laminated on the surface of a plastic, rubber, metal plate, glass, wood, slate or other substrate for the purpose of surface protection or decoration. More particularly, it relates to a fluorine resin type weather-resistant film which is excellent in the weather resistance, stain resistance, toughness such as chemical resistance, flexibility and adhesion to various substrates and which is particularly excellent in the bond durability after laminated on a substrate.
2. Discussion of Background
Heretofore, plastic plates, metal plates and various other substrates to be used as interior or exterior materials for buildings, used to be employed with their surface coated with coating materials or laminated with durable films (inclusive of those having printings applied).
The substrates to be subjected to surface treatment include plastic substrates such as polyvinyl chloride, polycarbonate, polymethyl methacrylate, an acrylonitrile-buthadiene-styrene copolymer and a fiber-reinforced plastic, various rubber substrates, metal substrates such as an aluminum-stainless steel-zinc steel plate, wood plates, glass plates and slates. Their applications extend to various fields including, in addition to wall papers and interior materials for elevators or vehicles, roof materials, wall materials, troughs, deck materials, garages, arcades, sun rooms, tents, agricultural materials, display boards, signboards, sound shielding walls, labels, window glasses, furnitures and house hold electric appliances.
Lamination of durable films to various substrates are usually conducted by means of various adhesives or heat lamination. Light is one of the main factors causing a problem of peeling, swelling or blistering at the bond interface. In either the case where various adhesives are used or the case where the bonding is conducted by heat lamination, an organic material such as a polymer material is present at least on one side of the bond interface. Particularly in the application to the exterior of buildings, such an organic material is subjected to irradiation of sunlight. Particularly the photon energy of the ultraviolet rays on the short wave length side is larger than the bond energy of molecules of the organic material, whereby the organic material tends to undergo rupture and degradation, and consequently the durability of bonding is hardly maintenable.
As a method for preventing the degradation of the organic material located at the bond interface, it is conceivable to impart a function of absorbing ultraviolet rays to the durable film itself. However, when the thickness of the durable film is thin, the production of a film having a good balance of various properties such as the physical strength of the film is technically difficult. Accordingly, a thick film is usually employed at the present. It is therefore desired to develop a durable film satisfying the above properties as soon as possible.
Heretofore, as durable materials, a coating material and film composed essentially of a vinylidene fluoride resin are known. For example, U.S. Pat. No. 3,454,518 discloses a coating material comprising methyl methacrylate (hereinafter referred to as PMMA), ethyl methacrylate and a vinylidene fluoride resin (hereinafter referred to as PVDF). Further, PVDF/PMMA/thermoplastic resin laminates are disclosed in Japanese Unexamined Patent Publication No. 59971/1976 and U.S. Pat. No. 4,272,585.
Further, U.S. Pat. Nos. 4,317,860, 4,415,519 and 4,444,826 disclose extrusion molded products of a PVDF/PMMA/thermoplastic resin. However, by any one of these methods, there has been obtained no film which is capable of being used for a long period of time as a weather-resistant product. Particularly, the interfacial bond strength between the PVDF layer and the PMMA layer is weak, and a peeling phenomenon is likely to result when the film is used for a long period of time.
It is an object of the present invention to provide a durable surface-protecting film excellent in the weather resistance, stain resistance, toughness such as chemical resistance, flexibility and adhesion to various substrates.
Another object of the present invention is to present a surface-protecting film excellent in the bond durability after lamination on various substrates.
The present inventors have conducted extensive researches to overcome the above problems. As a result, it has be found that when a multi-layer film comprising (1) a front surface layer made of a mixture of PVDF and PMMA and (2) a rear surface layer or an intermediate layer made of a mixture comprising PVDF, PMMA and an ultraviolet absorber, is laminated on a thermoplastic resin as a substrate, the interfacial bond strength within the multi-layer film as well as the interfacial bond strength between the multi-layer film and the thermoplastic resin substrate is strong, and (3) evaporation or dissipation of the ultraviolet absorber can thereby be prevented, whereby the thermoplastic resin layer can be protected for a long period of time.
Further, it has been found that by coloring the above multi-layer film with a composite oxide inorganic pigment and/or an inorganic pigment, when such a colored multi-layered film is laminated on a metal plate as a substrate, the interfacial bond strength between the colored film and the metal plate is strong and yet discoloration can be thereby prevented. The present invention has been accomplished on the basis of these discoveries.
Namely, the present invention provides:
1. A fluorine resin type weather-resistant film of multi-layer structure comprising a front surface layer made of a composition (A) comprising, as main components, from 50 to 95 parts by weight of a vinylidene fluoride resin and from 5 to 50 parts by weight of a methacrylate resin and a rear surface layer made of a composition (B) comprising, as main components, from 50 to 95 parts by weight of a methacrylate resin, from 5 to 50 parts by weight of a vinylidene fluoride resin and from 0.1 to 15 parts by weight of an ultraviolet absorber, wherein the overall thickness of the film of multi-layer structure is from 10 to 150 .mu.m, and the thickness of the front surface layer of the film is from 2 to 50 .mu.m.
2. A fluorine resin type weather-resistant film of multi-layer structure comprising a front surface layer and a rear surface layer both made of a composition (A) comprising, as main component, from 50 to 95 parts by weight of a vinylidene fluoride resin and from 5 to 50 parts by weight of a methacrylate resin and an intermediate layer made of a composition (B) comprising, as main components, from 50 to 95 parts by weight of a methacrylate resin, from 5 to 50 parts by weight of a vinylidene fluoride resin and from 0.1 to 15 parts by weight of an ultraviolet absorber, wherein the overall thickness of the film of multi-layer structure is from 10 to 150 .mu.m, and the thickness of the front surface layer of the film is from 2 to 50 .mu.m.
3. The fluorine resin type weather-resistant film according to item 1 or 2, wherein the film of multi-layer structure is colored with a composite oxide inorganic pigment and/or an inorganic pigment and has a covering power of at least 98% as represented by the contrast ratio calculated by the following formula from the values measured in accordance with JIS K-7105: EQU Contrast ratio=Y.sub.B /Y.sub.W .times.100 (%)
wherein Y.sub.B is the reflectance measured on a black substrate, and Y.sub.W is the reflectance measured on a white substrate.
Now, the present invention will be described in detail with reference to the preferred embodiments.
PVDF to be used for the composition (A) and the composition (B) in the present invention is a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride with a monomer copolymerizable therewith. The copolymerizable monomer may be, for example, ethylene tetrafluoride, propylene hexafluoride, chloroethylene trifluoride or vinyl fluoride.
PMMA is a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate with a monomer copolymerizable therewith, or a blend of polymethyl methacrylate and acrylate rubber. The copolymerizable monomer may be, for example, a C.sub.2 -C.sub.4 methacrylate, a C.sub.1 -C.sub.8 acrylate such as butyl acrylate, styrene, .alpha.-methyl styrene, acrylonitrile, acrylic acid or other ethylenically unsaturated monomer.
The ultraviolet absorber for the composition (B) in the present invention, may be any ultraviolet absorber so long as it is compatible with the resin to be used for the composition (B). To prevent the evaporation or dissipation, an ultraviolet absorber having a high molecular weight is preferred. As such an ultraviolet absorber, a benzotriazole type ultraviolet absorber, an oxalic acid type ultraviolet absorber, a benzophenone type ultraviolet absorber, a hindered amine type ultraviolet absorber and many other types of known ultraviolet absorbers may be employed. More specifically, 2-[3,5-di-(.alpha.-dimethylbenzil-2-hydroxyphenyl] benzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, 2-(3-t-butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole, 2-ethoxy-2'-ethyl oxalic acid bisanilide, 2-ethoxy-5-t-butyl-2'-ethyl oxalic acid bisanilide, 2-hydroxy-4-n-octoxy benzophenone, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl-2-(4-hydroxy-2,2,6,6-tetramethyl-1-piperidyl)ether, 1-[2-3-(3,5-di-t-butyl-4-hydroxyphenyl)propyonyloxy]-2,2,6,6-T-tetramethyl piperidine, may be mentioned.
As the main components for the composition (A) constituting the front surface layer and the rear surface layer of the present invention, PVDF and PMMA are employed, and the respective contents are from 50 to 95 parts by weight, preferably from 70 to 95 parts by weight, of PVDF and from 5 to 50 parts by weight, preferably from 5 to 30 parts by weight, of PMMA. If the content of PVDF exceeds 95 parts by weight, the adhesion to other layer tends to be poor, thus leading to feeling, such being undesirable. On the other hand, if the content is less than 50 parts by weight, the weather resistance tends to be low, whereby the effects as a protecting layer will be low, and blocking among the films tends to occur, whereby it becomes difficult to handle them as final products.
The content of an ultraviolet absorber in the front surface layer and the rear surface layer of the present invention is from 0 to 1 parts by weight, preferably from 0 to 0.5 part by weight, per 100 parts by weight of the total amount of PVDF and PMMA. If the content of the ultraviolet absorber exceeds 1 part by weight, the ultraviolet absorber is likely to bleed out on the surface of the film, whereby the interfacial bond strength with other film will be low, such being undesirable.
Next, as the main components for the composition (B) constituting the rear surface layer and the intermediate layer in the present invention, PVDF, PMMA and an ultraviolet absorber are employed. PMMA is from 50 to 95 parts by weight, preferably from 70 to 90 parts by weight, and PVDF is from 5 to 50 parts by weight, preferably from 10 to 30 parts by weight. If the content of PMMA is less than 50 parts by weight, the dispersion of the ultraviolet absorber tends to be inadequate, and evaporation or dissipation of the ultraviolet absorber is likely to take place, such being undesirable. On the other hand, if the content of PMMA exceeds 95 parts by weight, the bond strength between the front surface layer made of the composition (A) and the rear surface layer film tends to be poor, thus leading to peeling, such being undesirable.
The content of the ultraviolet absorber is from 0.1 to 15 parts by weight, preferably from 0.5 to 5 parts by weight, per 100 parts by weight of the total amount of PMMA and PVDF. If the content of the ultraviolet absorber is less than 0.1 part by weight, the quantity of the ultraviolet rays absorbed is small, whereby the performance as the protective layer will be inadequate. On the other hand, if the content exceeds 15 parts by weight, no additional effects will be obtained, and the cost increases.
The composition (A) and the composition (B) of the present invention may contain an antioxidant, a dispersing agent, a coupling agent, etc.
Further, the colorant to be used for coloring the composite film of the present invention, is preferably of an inorganic pigment type from the viewpoint of the weather resistance. For example, composite oxide type inorganic pigments may be used as the main color pigments, wherein two or more metal oxides form a new crystal structure by sintering and which are believed to develop colors by the decomposition of the crystal field. Typical composite oxide type inorganic pigments which are presently commercially available include a titanium yellow type having a rutile type or friedelite type crystal structure composed essentially of TiO.sub.2.Sb.sub.2 O.sub.3.BaO.NiO.Cr.sub.2 O.sub.3, a zinc-iron brown having a spinnel crystal structure composed essentially of ZnO.Fe.sub.2 O.sub.3.Cr.sub.2 O.sub.3, a cobalt-blue type having a spinnel crystal structure composed essentially of CoO.Al.sub.2 O.sub.3.Cr.sub.2 O.sub.3, a green type composed essentially of TiO.sub.2.CoO.NiO.ZnO, a black type having a spinnel structure composed of CuO.Cr.sub.2 O.sub.3 and CuO.Fe.sub.2 O.sub.3.Mn.sub.2 O.sub.3, and a violet type comprising CoO and Mn.sub.2 O.sub.3. Further, together with such color pigments, rutile type titanium oxide, zinc white, calcium carbonate, barium sulfate as well as other inorganic pigments, may be used.
As the covering power of the colored composite film, a covering power of at least 98% is adopted as a contrast ratio calculated from the values measured in accordance with JIS K-7105. The covering power is obtained by the following formula by a contrast ratio method based on the measuring method by A. H. Pfund (Reference is made to Shikisai Kagaku Handbook, compiled by Nippon Shikisai Gakkai and published on Jul. 31, 1980): EQU Contrast ratio=Y.sub.s /Y.sub.W .times.100 (%)
wherein Y.sub.B is the reflectance measured on a black substrate, and Y.sub.W is the reflectance measured on a white substrate.
If the contrast ratio is less than 98%, light enters through the colored film and reaches the bond interface between various materials, whereby degradation of the organic material at the interface will be caused, and the bond strength is likely to be lowered.
As a method for coloring the composite film, there may be employed either a method of coloring all the layers or a method of coloring only one layer, so long as the above contrast ratio will be at least 98%. The amount of the composite oxide inorganic pigment or an inorganic pigment is dependent upon the contrast ratio and is not particularly limited. However, taking the color tone (the composition of the pigment) into consideration, such a pigment is preferably used in an amount of from 1 to 50 parts by weight per 100 parts by weight of the overall resin composition of the composite film.
The weather-resistant film of the present invention is composed at least of two layers i.e. the front surface layer and the rear surface layer. But, it may be made into a multi-layer film wherein the composition (B) containing the ultraviolet absorber and the composition (A) containing no such ultraviolet absorber are disposed alternately to each other. Further, the weather-resistant film of the present invention has a thickness within a range of from 10 to 150 .mu.m, preferably from 10 to 100 .mu.m as the thickness of the entire film of multilayer structure. If the thickness of the film is less than 10 .mu.m, the whether resistance of the multi-layer film tends to be low, and degradation of the material is accelerated, and a substantial amount of an inorganic pigment has to be added to accomplish the covering power of at least 98% as the contrast ratio of the coloring, whereby the physical strength as the film will be impaired, and thus the film is practically useless. On the other hand, if the thickness of the film exceeds 150 .mu.m, no further remarkable improvement of the weather resistance is obtainable, and the cost of the multi-layer film increases.
Further, with respect to the ratio in the thickness of the multi-layer film, the front surface layer film is from 2 to 50 .mu.m. If the front surface layer film is less than 2 .mu.m, the weather resistance, stain resistance and chemical resistance tend to be low. On the other hand, even if the thickness exceeds 50 .mu.m, no further remarkable effects are obtainable, and the cost increases. Whereas, the film made of the composition (B) containing an ultraviolet absorber, it preferably at least 20% of the entire thickness of the multi-layered film. If it is less than 20%, the effects as a surface-protecting performance to prevent degradation of the substrate, tend to be low.
A weather-resistant film of the present invention may be used for various applications with the front surface layer having subjected to printing. Further, for the bonding of the weather-resistant film of the present invention to various substrate, common adhesives of e.g. epoxy resin type, acrylate resin type or urethane resin type, can be used. Further, a pressure sensitive adhesive using natural rubber of an acrylate resin, may preliminarily coated on the bond surface of the weather-resistant film before use. Depending upon the type of the substrate, the bonding may simply be conducted by heat treatment only.
The fluorine resin type weather-resistant film of the present invention can be extruded by means of a co-extrusion molding method whereby a plurality of layers are usually integrally bonded.
It is also possible to use a T-die wherein a plurality of extrusion molding machines are employed to bond resins in a molten state to form a multi-layer structure. The co-extrusion molding method includes a method using a multi manifold die wherein a plurality of resin layers are formed into sheets and then brought in contact to one another for bonding, and a method wherein a plurality of resins are bonded and then stretched into a sheet form. Further, a multi-layer film may be formed by a so-called inflation molding method wherein a round die is employed. To incorporate additives such as an inorganic pigment, a ultraviolet absorber, etc. to the layer comprising PVDF and PMMA as resin components, a method of preliminarily mixing the resins and the additives, followed by melt-kneading by means of a commonly employed single screw extruder, may be employed. However, by such a method, the distribution of the additives into the resin tends to be inadequate. Therefore, it is preferred to employ a twin screw extruder of high kneading performance, whereby starting material having excellent surface condition can be provided. As a method for further improving the dispersibility, a part or whole of PVDF and/or PMMA may be used in a power form.